1. Field of the Invention
This invention relates to the use of coiled tubing in a well, and more particularly, to a tapered connector for joining lengths of coiled tubing with differing outside diameters.
2. Description of the Prior Art
After a well has been completed to produce oil or gas, it is necessary to periodically service the well. There are many occasions where the service procedure is carried out using coiled tubing. Such tubing is inserted into the wellhead through a lubricator assembly or stuffing box. Typically, this is necessary because there is a pressure differential at the surface of the well and the atmosphere, which may have been naturally or artificially created, that serves to produce oil or gas or a mixture thereof from the pressurized well. The tubing is inserted by an injector which generally incorporates a tubing guide, or gooseneck, and a plurality of gripper blocks for engaging the tubing and moving it through the injector. One such injector apparatus is shown in U. S. Pat. No. 5,553,668, assigned to the assignee of the present invention.
The tubing is relatively flexible and can therefore be cyclically coiled onto and off of a spool, or reel, by the injector which often acts in concert with a windlass and a power supply which drives the spool or reel. In the injector, the gripper blocks are attached to movable gripper chains. The gripper blocks sequentially grip the coiled tubing that is positioned therebetween. When the gripper chains are in motion, each chain has a gripper block that is coming in contact with the coiled tubing as another gripper block on the same gripper chain is breaking contact with the coiled tubing. This continues in an endless fashion as the gripper chains are driven to force the tubing into or out of the wellbore, depending on the direction in which the drive sprockets are rotated.
In the past, such coiled tubing has had a constant cross section. However, maintaining a constant diameter for the tubing can present some problems under certain circumstances. For example, it may be desirable to reduce the weight of the string, and this cannot be done if the string has a constant diameter. Further, a larger string causes more drag in the wellbore, particularly when the strings are being used in a horizontal or other deviated portion of the well. There is a need, therefore, for a tubing string with different sized portions. The present invention provides a solution to this problem by providing a string having a tapered connection therein between two lengths of tubing having differing diameters. This is accomplished by providing a tapered connector which provides an elongated tapering tubing string portion which is connected at opposite ends thereof to a larger tubing portion and a smaller tubing portion.
For example, a larger outside diameter tubing at the top of the string and a smaller outside diameter tubing at the bottom allow the coiled tubing string to be designed for longer lengths by reducing the hanging weight of the string and also reduces the percent of yield load on the larger diameter portion compared to a string having a single outside diameter.
The present invention also provides for use of a smaller outside diameter portion in a horizontal or deviated well formation, thus reducing the drag of the tubing while still having the larger diameter portion at the top of the string to push the string further into the well because of the decreased buckling of the large portion.
Another problem with constant diameter tubing relates to the key issue of pressure drop therethrough. If the wellbore size at the treatment area is small, then previously a small diameter length of tubing had to be used. The smaller diameter tubing could present significant pressure drop problems. The present invention solves this by allowing the use of larger outside diameter tubing close to the treatment zone with a smaller portion actually at the treatment zone.
All of these embodiments are possible due to the V-shaped groove design of the gripper blocks in the Halliburton injector system which allows tubing of varying outside diameters to be engaged by the same blocks.
The apparatus of the present invention utilizes one or more tapered connectors in a tubing string for use in servicing a well. Thus, the invention provides a tubing string for use with a tubing injector for injecting tubing into a wellbore wherein the string comprises at least a first tubular portion having a first tubing outside diameter, a second tubular portion having a second tubing outside diameter which is different than the first tubing outside diameter, and a tapered portion disposed between the first and second tubing portions. The tapered portion comprises a first end having a first end outside diameter substantially equal to the first tubing outside diameter and a second end having a second end outside diameter substantially equal to the second tubing outside diameter. The tapered portion is preferably substantially conical.
The tapered portion may be connected to the first and second tubing portions by a variety of means. For example, it can be crimped, swaged, screwed or welded to the connection. A first connector may be used interconnecting the first tubing portion and the first end of the tapered portion, and a second connector may be used interconnecting the second tubing portion and the second end of the tapered portion. These first and second connectors may be integrally formed with the tapered portion. Multiple tapered portions with connectors may be utilized in a tubing string to connect differing diameter tubings into a string for servicing a well.
In the preferred embodiment, the first and second connectors are substantially cylindrical. The first connector has a first connector outside diameter substantially equal to the first tubing outside diameter, and the second connector has a second connector outside diameter substantially equal to the second tubing outside diameter.
The present invention also includes a method of running tubing in a wellbore comprising the steps of (a) providing a tubing string having an outer surface with a plurality of outside diameters, and (b) injecting this tubing string into the wellbore. Step (a) comprises providing the tubing string with a tapered connector between adjacent tubing portions having different outside diameters. Step (b) comprises passing the tapered connector through a tubing injector for injecting the tubing into the wellbore. This injector is provided with a plurality of gripper blocks therein adapted for engaging and gripping the tapered connector and the different outside diameters of the tubing string as the tubing string is injected into the wellbore.
Stated in another way, the invention includes a method of running tubing into a wellbore comprising the steps of (a) positioning a tubing injector adjacent to a wellhead at an upper end of a wellbore, (b) positioning a tubing string through the injector, the tubing string being provided with an outer surface having more than one outside diameter, and (c) actuating the tubing injector for injecting the tubing string in the wellbore. Step (c) may include passing a tubing connector therethrough which interconnects the portions of the tubing string having different outside diameters.
Numerous objects and advantages of the invention will become apparent with the following detailed description of the preferred embodiment is read in conjunction with the drawings illustrating such embodiment.